Automobile Inspection Technology

Chapter 32 Vehicle Inspection Technology (8)
According to the national standard GB18285-2000 "Limits and Test Methods of Exhaust Pollutants from Automobiles in Use", for vehicles equipped with compression ignition engines, it has passed the national standard GB14761-2001 "Limits and Test Methods of Exhaust Pollutants from Automobiles" Vehicles with Category C certification shall be subject to the free acceleration exhaust visible pollutant test, except for vehicles equipped with compression ignition engines that have passed the Category C certification, shall be subject to the free acceleration smoke test.It is also stipulated that the free acceleration exhaust visible pollutant test shall be carried out in accordance with the national standard GB18285-2000 "Exhaust Pollutant Limits and Test Methods of Vehicles in Use" Appendix B, and the free acceleration smoke shall be in accordance with the national standard GB/T3846-1993 "Diesel Vehicle The free accelerated smoke measurement is carried out according to the Filter Paper Smoke Method.

According to the national standard GB18285-2000 "Limits and Test Methods of Exhaust Pollutants of In-Use Automobiles", for in-use vehicles equipped with compression ignition engines, the maximum total mass is greater than or equal to 400kg, and the maximum design speed is greater than or equal to 50km/h. For vehicles, see Table 5-20 for the smoke emission limits of the free acceleration test.

2. Detection of exhaust pollutants from diesel vehicles

The national standard GB/T3846-1993 "Measuring Filter Paper Smoke Method for Diesel Vehicle Free Acceleration Smoke" stipulates that when detecting diesel vehicle exhaust smoke, filter paper smoke meters should be used, and the testing conditions and measurement procedures are specified. Regulation.

(1) Basic detection principle

The measurement principle of the filter paper smoke meter: use a piston type air pump to extract a certain volume of exhaust gas from the exhaust pipe of the diesel engine, so that it passes through a certain area of ​​white filter paper, and the carbon smoke in the exhaust gas remains on the filter paper. Make it black.Use the detection device to measure the blackness of the filter paper, and then indicate it with the indicator device.The blackness represents the exhaust smoke of diesel vehicles.

Structure and working principle of filter paper smoke meter
Filter paper smoke meter is one of the most widely used smoke meters. It has three forms: manual, semi-automatic and fully automatic. Its structure is composed of exhaust gas sampling device, blackness detection and indicating device and control device, such as As shown in Figure 5-48.

①Exhaust gas sampling device.The exhaust gas sampling device consists of a sampling probe, a piston pump and a sampling hose.

Sampling probes are divided into two types: bench test and vehicle test.The sampling probe for the whole vehicle test has a heat sink, and a clamp is installed on it to fix it on the exhaust pipe.The sampling probe extracts the exhaust gas under the action of the piston air pump, and its structure and shape should ensure that the sampling will not be affected by the exhaust pressure.

Piston type suction pump is composed of piston pump, handle, return spring, locking device, solenoid valve and filter paper clamping mechanism, etc.Before sampling, manually or automatically press down the handle of the air pump until the piston reaches the bottom end overcoming the tension of the return spring and is locked by the locking mechanism; when sampling is required, depress the foot switch or press the "manual pump ” button, the solenoid valve can be operated to release the compressed air from the locking mechanism to the piston, and the piston rises to the top under the tension of the return spring to complete the sampling process.

The filter paper clamping mechanism realizes the clamping and sealing of the filter paper during sampling, so that the exhaust gas during the sampling process enters the pump barrel through the filter paper, and the carbon smoke remains on the filter paper to stain it black, and can ensure the effective working surface of the filter paper The diameter is 32mm.After the sampling is completed, the filter paper clamping mechanism is released, and the blackened filter paper is sent to the blackness detection device by the feeding mechanism.

The sampling hose connects the sampling probe and the piston pump. Since the pumping volume of the pump is related to the volume of the hose, the national standard stipulates that the length of the sampling hose is 5.0m, and the inner diameter is -0.2mm. The local inner diameter of the sampling system is Not less than 4mm.

② Blackness detection and indication.It is composed of photosensitive sensor, indicating instrument or digital display, filter paper and standard smoke sample, etc.The photosensitive sensor is composed of a light source (incandescent bulb), a photoelectric element (annular smashed photocell), etc.The working principle is shown in Figure 5-49.After the power is turned on, the incandescent bulb is bright, and its light shines on the filter paper through the ring-shaped photocell with a central hole. When the blackness of the filter paper is different, the light intensity reflected to the photosensitive surface of the ring-shaped photocell is also different, so the ring-shaped photocell The photocurrent generated by the photocell is also different.

The indicating ammeter is a microammeter, which is an indicating device for the degree of blackness of filter paper, that is, the degree of exhaust smoke.When the photocurrents sent by the ring-shattered photocells are different, the positions of the ammeter pointers are also different.Indicating gauge head is indicated by -Qin 10.Where 0 is only 6 units of all white filter paper,

10 is the R6 unit of all black filter paper, evenly distributed from 0-10.

The detection device is generally equipped with a standard smoke sample for calibration or calibration and a filter paper that meets the requirements.The standard smoke sample, also known as the smoke card, should be calibrated on the smoke meter with an accuracy of 0.5%.When the standard smoke sample is used to calibrate the smoke meter, the uniform distribution according to the range shall not be less than 6; when it is used to calibrate the smoke meter, 3 samples shall be used for each smoke meter, and the calibration value shall be around R5.When the smoke meter indicator needs to be calibrated, just put the standard smoke sample under the photosensitive sensor, and use the adjustment knob to adjust the pointer of the indicating ammeter to the blackness value represented by the standard smoke sample to achieve the goal.This allows the indicating instrument to maintain indicating accuracy for accurate measurements.The smoke meter must be calibrated regularly and can only be used within the validity period.

There are two types of filter paper, ribbon and disc.The belt-shaped filter paper can be continuously conveyed under the action of the feeding mechanism, which is suitable for semi-automatic and fully automatic smoke meters.Disc filter paper, only suitable for manual opacimeters.

③Control device.The control device includes an electromagnetic foot switch of the air pump operated by feet, a filter paper feeding mechanism and a compressed air cleaning mechanism, etc.The compressed air cleaning mechanism can use compressed air to clean the residual exhaust gas carbon particles in the sampling probe and sampling hose before exhaust gas sampling.

⑤ Then run at idle speed for about 16s.During this period, use compressed air to blow the sampling hose and sampling probe for 3-4s.

⑥Fix the pedal switch on the accelerator pedal or hold the manual rubber ball in your hand.

⑦ Depress the accelerator pedal and the pedal switch to the bottom quickly, or press the manual rubber ball rapidly while depressing the accelerator pedal, and release the accelerator pedal and the pedal switch quickly after 4 seconds.

⑧Keep running at idle speed for 16s.During this period, the piston of the suction pump is pressed down to the starting position of suction, and the smoke meter with paper roll can complete the paper feeding and the smoke value can be read directly from the meter head.During this period, the sampling hose and sampling probe should be blown with compressed air for 3-4s.

⑨Depress the accelerator pedal and the pedal switch again, the time interval between the two times is 20s, repeat the sampling in this way 4 times, do not measure the first sampling, and the arithmetic mean value of the last three readings is the exhaust gas under this working condition Smoke value.

(Section VIII) Vehicle Noise Detection

Noise comes from many sources, including traffic noise, industrial noise and living noise.Among them, traffic noise has more and more influence on people's daily life, and car noise is the main component of traffic noise, and noise is the second public hazard of cars.With the development of motor vehicles towards high speed and high power, traffic noise has become the main noise source in some big cities.car noise

(3) Detection method of free acceleration smoke of diesel vehicles

According to the provisions of GB/T3846-1993, the detection of free acceleration smoke of diesel vehicles should be carried out under free acceleration conditions, using a filter paper smoke meter according to the measurement regulations.The free acceleration condition refers to: the engine is in the idling condition (the clutch is in the engaged position, the accelerator pedal is in the released position, the shift lever is in the neutral position when the mechanical or semi-automatic transmission is installed, and the selector is in the parking or neutral position when the automatic transmission is installed. ), quickly depress the accelerator pedal to the bottom, hold it for a few seconds and then release it.

The detection steps are as follows:
①Fix the sampling probe in the exhaust pipe against the airflow direction, and make its center line parallel to the axis of the exhaust pipe.

②Introduce the pedal switch into the cab of the car or introduce the manual rubber ball into the cab of the car through the remote control hose.

③ Press the air pump piston into the lock card.

④ According to the measurement procedure shown in Figure 5-50, carry out free acceleration smoke detection.Depress the accelerator pedal to the bottom from the idling condition, and then release it quickly after about 4 seconds. Repeat this three times to blow off the carbon residue in the exhaust pipe.

Mainly include: engine mechanical noise, fuel noise, intake and exhaust noise and fan noise; chassis mechanical noise, brake noise and tire noise, cabin vibration noise, cargo impact noise, horn noise and beeps when turning and reversing Wait for the noise.Among these noises, the noise level is mostly related to the use of the vehicle. When the vehicle accelerates, decelerates and brakes, overspeeds, overloads and the road surface is uneven, the noise increases significantly.

[-]. Vehicle noise and its hazards

1. Overview of car sounds
Car noise is divided into two types: exterior noise and interior noise.The noise outside the car causes environmental pollution, and the noise inside the car directly causes damage to the driver and passengers.Car noise must be studied and measured for noise reduction.A car is assembled from many parts or mechanical assemblies.During the operation of the car, it is affected by the internal combustion engine and mechanical transmission mechanism and the impact from the road surface. All parts will generate vibration and noise. In fact, the car is a complex complex including various types of noise.

noise source.

Car noise can be roughly divided into the following categories according to its nature:
① Burning noise.It refers to the noise generated by the periodic change of the gas pressure in the cylinder when the internal combustion engine is working.

②Intake and exhaust noise.It refers to the noise generated when the gas flows through the intake pipe and exhaust pipe at high speed when the internal combustion engine is working.

③ Fan running noise.

④Mechanical noise.This refers to the noise generated by the periodically changing force between various mechanical moving parts in the car and between the moving body and solid parts when the car is running.

⑤ Tire noise.Including when the tires of the car are rolling on the ground, the air noise caused by the air flow between the tire treads and the air disturbance around the tires, the vibration noise caused by the elastic deformation vibration of the tire carcass and the treads, and the gap between the tires and the road due to the uneven road surface. The impact noise (this kind of vibration and impact noise will also appear louder when the vehicle makes a sharp turn or brakes suddenly).

⑥ Body noise.When the car is running, the friction and impact of the body and the air, and the wall structure of the car body will also generate vibration noise under the vibration excitation of the engine and the uneven road surface.It is one of the main reasons for the interior noise of various passenger cars and truck cabs.

According to the process of noise generation, car noise sources can be roughly divided into two categories: one is the noise related to the operation of the internal combustion engine; the other is the noise related to the driving of the car.The noise related to the operation of the internal combustion engine mainly includes combustion noise, mechanical noise, cooling fan noise, intake and exhaust noise, and various accessories (such as compressors, generators, etc.) noise.The noise related to automobile running mainly includes: mechanical noise of transmission mechanism (transmission, drive shaft, differential, etc.), noise from tires, vibration of vehicle body (frame) and noise generated by air interaction.

2. Harm of noise

Noise affects human beings in all aspects of physiology, psychology and society.Working and living in a high-noise environment for a long time is harmful to human health, even if the noise level is low, it will interfere with people's normal activities.Its hazards and impacts generally have the following aspects:

① cause a variety of diseases.The first is damage to the auditory organs.The impact of noise on hearing is related to its sound pressure level, frequency and action time.Mild cases can cause temporary deafness, that is, it takes a period of time to restore the original hearing from a strong noise environment to a relatively quiet place.Severe cases can produce noise-induced deafness.According to international statistics, when the noise level is 90dB(A), deafness
The incidence rate reaches 21%, and the rate of 100dB(A) can be as high as 40%.

Other loud noises can cause psychosis and even be life-threatening.Noise can also induce adverse effects on the nerves, heart, and digestive system, manifested as dizziness, headache, insomnia, nervousness, rapid heartbeat, elevated blood pressure, coronary heart disease, indigestion, and vomiting.According to relevant data surveys, people live in a noise environment above 95dB for a long time, and 10% of them will cause neurasthenia, mental illness, and increase blood pressure.

②Affect people's normal work and rest.The noise is above 90dB(A), and the frequency is higher than 1000Hz, and the influence is obvious.It is easy to cause fatigue, poor sleep, decreased work efficiency and other hazards.Tests and investigations have shown that when the sound pressure level is 40-45dB(A), normal sleep is disturbed, and the degree of influence reaches 10%-20%.Seriously affect work efficiency when reaching HdB(A).When the sound pressure level is 75dB(A), normal conversation is difficult at a distance of 0.3m.

③ Affect traffic safety.Living in a noisy environment for a long time makes drivers and pedestrians prone to fatigue, distraction, inattention, etc., which easily induces traffic accidents.

[-]. Vehicle noise testing standards and testing methods

1. Vehicle noise inspection standards

The national standard GB7258-2004 "Technical Conditions for the Safety of Motor Vehicle Operation" stipulates the noise level inside the passenger car, the noise level next to the driver's ear and the sound level of the horn of the motor vehicle, and GB1495-2002 "The limit value and "Measurement Method" stipulates the maximum noise level outside the vehicle and its measurement method.

Maximum allowable noise level outside the vehicle
See Table 5-21. When the car is accelerating, the maximum allowable noise level outside the car should meet the requirements in the table.The maximum permissible noise level outside the vehicle when accelerating for deformed or refitted vehicles (except fire trucks) of the various types of vehicles listed in the table shall comply with the noise regulations for basic vehicles.

(4) Motor vehicle horn sound level

When the horn sound level is measured at a distance of 2m from the front of the car and 1.2m from the ground, the value should be 90-115dB.

2. Detection of car noise

In the measurement method of automobile noise, the instrument used in the national standard is a precision sound level meter or an ordinary sound level meter.

(1) The structure and working principle of the sound level meter

The sound level meter is a kind of noise that can approximate the hearing characteristics of the human ear

An instrument for measuring its noise level.It can be used to detect the driving noise, exhaust noise and horn sound level of motor vehicles.

According to the different measurement accuracy, the sound level meter can be divided into two types: precision sound level meter and ordinary sound level meter; according to the different power supply used, it can be divided into two types: AC sound level meter and DC sound level meter, the latter can also be called The portable sound level meter has the characteristics of small size, light weight and convenient on-site use.

A sound level meter generally consists of a microphone, an amplifier, an attenuator, a weighting network, a detector, an indicating meter, and a power supply.Working principle: The measured sound wave is converted into a voltage signal through the microphone (device), attenuated or amplified according to the signal size, the amplified signal is sent to the weighting network for processing, and finally detected and indicated in dB scale The noise value is indicated on the meter head.Figure 5-51 is the outline drawing of the ND2 precision sound level meter produced in my country.

(2) Detection method of automobile noise

① Exterior noise detection.The schematic diagram of the noise measurement site is shown in Figure 5-52.The runway of the test site should be a straight, dry asphalt or concrete pavement with a slope not greater than 0.5%.The microphones of the sound level meter are arranged on both sides of the center point of the 20m runway, each is 7.5m away from the center line of the center HA, and 1.2m above the ground, and the axis of the microphone is parallel to the
road and perpendicular to the direction of vehicle travel.The test site should be open,

There should be no large reflectors, such as buildings, walls, etc., within the radius of 25m from the test center.When the vehicle under test is not running, the noise of the surrounding environment measured at the test site should be at least 10dB lower than the noise of the vehicle under test, and the measurement should not be disturbed by accidental other sound sources.In order to avoid the interference of wind noise, it is best to measure under the condition of zero wind speed, or use a windshield, but attention should be paid to the influence of the windshield on the sensitivity of the sound level meter.When measuring, there should be no other people near the sound level meter, and the measurer should be at least 0.5m away from the sound level meter to reduce the measurement error caused by human body reflection.The vehicle under test is unloaded during the test, and a full-load test can be carried out if necessary.Other auxiliary equipment on the car is also a source of noise, as long as it is used frequently, it should be activated during measurement.

——加速行驶车外噪声的测量。车辆经走热后，按规定条件：前进挡位为4个挡位以上的车辆用第三挡；前进挡位为4个挡或4个挡以下的车辆用第二挡；对于自动换挡车辆使计权网络，分别读取表头指针最大读数的平均值。如果做车内噪声频谱分析，应包括中心频率为31.5Hz、63Hz，125Hz、250Hz、500Hz、l000Hz、2000Hz、4000Hz、8000Hz的倍频带声级。

Use the gear with the fastest acceleration in the test area.The engine speed is 3/4 of the rated speed.When there is no tachometer, the vehicle speed corresponding to the gear speed can be used to control, and the vehicle drives to the end line at a constant speed of 50km/h.When you reach the starting line, immediately depress the accelerator pedal to the bottom and accelerate straightly.When the rear end of the vehicle reaches the terminal line, stop accelerating immediately.

The measurement requires the engine under test to reach the rated speed in the rear half region.If this requirement cannot be met, the lines at both ends of the test site can be extended outward by 7.5m.If the requirements are still not met, the vehicle gear should be lowered by one gear.If the vehicle exceeds the rated speed in the second half area, the linear speed at the beginning can be appropriately reduced.

The sound level meter is measured with the "A" weighting network "fast" gear, and the maximum reading of the sound level meter head is read when the vehicle passes by.

(End of this chapter)